shallow foundation part 4-in situ testing and settlement on sand

7/21/2019 Shallow Foundation Part 4-In Situ Testing and Settlement on Sand

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Shallow Foundation- In Situ Testing and Settlement on

Sand

Dr. Kok Sien Ti


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The main purpose of the test is to provide an indication of the relativedensity of granular deposits, such as sands and gravels from which it isvirtually impossible to obtain undisturbed samples.

The great merit of the test, and the main reason for its widespread use

is that it is simple and inexpensive.

The soil strength parameters which can be inferred are approximate,but may give a useful guide in ground conditions where it may not bepossible to obtain borehole samples of adequate quality like gravels,

sands, silts, clay containing sand or gravel and weak rock.

Standard Penetration Test (SPT)


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In this dynamic test, an open ended split-spoon sampler is driven intothe bottom of a borehole by means of a 65 kg trip hammer fallingthrough 760mm.

The sampler is initially driven 150mm into the sand to seat the device,

then the number of blows N to advance the device a further 300mm isrecorded. This is done in 4 increments of 75mm.

N=Standard Penetration Resistance.

If testing in gravels, the driving shoe is replaced by a solid 60 cone.

Procedures


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Sample SPT logs


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The standard practice now in the U.S. is to express theN-value to anaverage energy ratio of 60% ( N60).

Thus, correcting for field procedures and on the basis of fieldobservations, it appears reasonable to standardize the field penetrationnumber as a function of the input driving energy and its dissipationaround the sampler into the surrounding soil, or


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Burland and Burbage (1986) Method for

Settlement


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Example:


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Cone Penetration Test (CPT)


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The tip resistance is theoretically related to undrained shear strength ofa saturated cohesive material, while the sleeve friction is theoreticallyrelated to the friction of the horizon being penetrated (Robertson andCampanella, 1986).

The local friction measures the average skin friction as the probe isadvanced through the soil.

The friction ratio is the ratio of skin friction divided by the tipresistance (both in tsf ), given in percent. It is used to classify the soil by

its behavior or reaction to the cone being forced through the soil.

Cone Penetration Test (CPT)


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Sample CPT logs


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Calculating Elastic Settlement on

Sand from CPT Data


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Example:


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shallow foundation part 4-in situ testing and settlement on sand

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